ADJE WebMail is a set of Perl CGI scripts which provide a Web interface to
existing email accounts on any POP3-compliant email server. The software
provides a complete interface, including encoding/decoding attachments, email
and URL markup in received emails, and an address book for each user.

AeroMail is a Web-based email client that uses an
IMAP server to read and store messages in one or
more user-defined folders. Features include: HTTP
authentication for login (no cookies) or login
with cookies; Optional IMAP folder manipulation;
optional spam flagging using reverse DNS mapping;
HTML messages and attachments; simple HTML that
can be embedded in a page of your own design;
support for different character sets (e.g. Russian
and Chinese); support for SSL IMAP servers; and
support for sendmail's genericstable (reverse
mapping of users for outbound mail). JavaScript is
not necessary.

AfterLogic WebMail Lite PHP is a Webmail script with a modern AJAX interface. It supports IMAP accounts, SMTP, and SSL (including Gmail). Users can check and send mail and use an address book. It provides a slick skin, a three-pane view, non-English language support, UTF-8 support, IMAP folders, and viewing and composing HTML mail. A MySQL backend is supported, with Web-based administration and installation and cPanel/Plesk/DirectAdmin integration.

AlphaMail is a mod_perl webmail system with a C++ middleware component that is intended to make the system highly scalable. It supports many Unix variants with any RFC-compliant IMAP server (including UW, Cyrus, and Dovecot).

Althea is an IMAP email client for X that uses the GTK widget set. It was built with the IMAP protocol in mind in order to avoid many of the pitfalls experienced by POP clients that added IMAP support. Althea allows easy access to a nearly unlimited number of servers, and has a very small memory footprint. As of version 0.5.0 Althea also supports IMAP over SSL.

The AmavisNewSQL SquirrelMail plugin gives you
per-user control of a subset of SpamAssassin
settings which are stored in a database. It also
allows you to use a quarantine database for
questionable mail. This plugin was designed with
enterprise use in mind, and differs from other plugins in that it works with amavis-new
rather than SpamAssassin directly. Most of the
code lives in an external class that you can reuse
in your own admin tools. It even has support for
SOAP calls to perform common tasks.

Arrow is an elegant, powerful, graphical interface to electronic mail. This is not just another single window mail reader. Instead, it displays each mailbox and message in a separate window, thereby allowing one to simultaneously open as many mailboxes and view and compose as many messages as one wishes. This paradigm also allows one to drag-and-drop text between messages and organize ones mail by dragging messages between mailboxes.